Modder here!This fourm!This going to help my build alot

Discussion in 'Introduce Yourself' started by Florida_Trail_Rider, Mar 4, 2013.

  1. Hello I just joined with you guys you should see me around Check out my build Ill update more I only have 2 crappy pics right now.
    26in Specialized hard rock pro with 66cc,Jackshaft kit.I ported the head,intake and exhaust looking to upgrade carb if anyone knows one that really runs good on the 66cc(80cc).Also have 2 steet tires im doubling up on the back.Just got the engine fit perfect there is no room and so its been fun.
    Nick
     

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  2. Fabian

    Fabian Well-Known Member

    There is nothing wrong with the standard NT once it is jetted correctly.
    I have tried all of float style carburettors and returned to the NT, until Rock Solid Engines released their (reed valve compatible) Walbro style (diaphragm) carburettor.

    There is no going back to a float style system once you've used a diaphragm carby.
     
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  3. roughrider

    roughrider Member

    I agree. I mean, really, a carb is a simple device that is supposed to mix air with fuel. It's not that complicated. One of my mechanic friends--who owns a smog shop--was laughing with me about how everyone thinks a carb is SO IMPORTANT and must be the cause of ALL THEIR PROBLEMS!

    It's not. It's just a link in the chain. The stock carbs are actually pretty reliable and easily tuned. I say this after messing with a "performance" carb and finding it was a huge waste of time.
     
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  4. Fabian

    Fabian Well-Known Member

    Even a diaphragm carburettor compared to the NT float style carburettor (identical venturi size for identical venturi size) will produce no more power because a 14mm hole is a 14mm hole regardless of the manufacturers brand name.

    The big difference with a diaphragm carburettor is ease of tuning as they have externally adjustable jetting screws, allowing air/fuel ratio adjustment on the fly and under load; making for easy adjustment; a very handy feature if atmospheric conditions change significantly from one day to the next or in some cases from one hour to the next.

    No more needing to pull the d.a.m.n fuel bowl off, spilling fuel all over your hands and the bike, just to change the main jet, only realising that the jetting change didn't get you into the butter zone, and you have repeat the process; sometimes 3 or 4 times till you get it spot on; then atmospheric conditions change, requiring the process to be done all over again.

    I just hate this process with a passion, and a diaphragm carburettor makes the tuning process such a breeze.

    Once you've used a Walbro style carby, you'll never go back to a float style carby.
     
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  5. roughrider

    roughrider Member

    It's something I'd like to try, for sure.

    I was just reading up on that type of carb. One of my books is Mark Zimmerman's Motorcycle Maintenance. He says that the diaphragm type (which he call "CV," or "constant-velocity") carbs were originally developed to overcome the slide type carbs tendency to make an engine stumble when the gas was hit too hard and fast. Then too, they are useful for applications like saws and trimmers, for they can run in any position.
     
  6. Fabian

    Fabian Well-Known Member

    and diaphragm carburettors don't seem to suffer from fuel leaks or air leaks - they just work!
     
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  7. Thanks I like the simple stock carb anyways, just wondering..Just started building this engine so I have to see what it likes.Any good websites with mod tips would be loved :bowdown:
     
  8. Fabian

    Fabian Well-Known Member

    Heaps of mod tips on this website. Just use the search function.
     
  9. jaguar

    jaguar Well-Known Member

    Click onto my signature link for modification info.
    The trouble with the NT carb is adjustability. There is no dedicated low rpm mixture path and so the idle gas comes up via the needle which is a crude way to do it and the mixture isn't as finely mixed as it is in a carb with a dedicated idle mixture circuit. You can adjust the idle mixture via the height of the needle. And you can change the high rpm jetting by resizing the hole in the main jet with solder and a micro drill bit. But there is no way to adjust the mid range mixture. Any other carb works better than the NT.
    I think you should consider the Mikuni 16mm which wants to clamp onto something 20mm OD. I have jetting suggestions for it on my site. And definitely stay with an extended intake path until the day you get a reed valve (which isn't advised unless you also get an expansion chamber).
     
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  10. Fabian

    Fabian Well-Known Member

    My bike uses a reed valve and the exhaust is stock standard. An expansion chamber might make for greater torque or power, depending on the type of expansion chamber, but the reed valve intake (on it's own) significantly boosted low and midrange torque, even with the standard exhaust system.
     
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  11. jaguar

    jaguar Well-Known Member

    When I was testing I preferred the power of an intake extension on a piston port intake over a reed valve w/o expansion chamber.
     
  12. Fabian

    Fabian Well-Known Member

    That may be the case but the intake extension would do nothing to reduce the noise coming from the intake tract.
    The reed valve intake does not only one, but two things: it improves low and midrange torque and noticeably decreases intake noise, making the engine sound more civilised and simply more pleasant to ride.
     
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  13. jaguar

    jaguar Well-Known Member

    That is true about the intake noise but a good custom filter box can reduce that. I can't say with all certainty that an intake extension is always better than a reed valve for low rpm grunt but with my bike that was the case.
     
  14. I looked over your mod link Jag,for a good hour last night.So much good stuff!
    I'm worried though I raised my needle 1 notch from stock so I can just try to idle it down and hope for the best,Probably going to run way to rich until I get the chamber and better carburetor my new pull starter is coming in the mail today..Im going for the expansion chamber first then the reed valve so I can try something better then this stock carburetor.

    P.S. Jaguar..Your the man!:bowdown: I hope to get a part of your knowledge on these engines as fast as possible I love them and its on my bmx mountain bike with the jack-shaft kit makes it so much cooler..Last question-Were can I get the NGK besides the net,Would auto zone carry it?I live out in the country its never good to waste the gas going into city to find they don't have it:sweatdrop:
     
  15. jaguar

    jaguar Well-Known Member

    yeah they have NGK. also my favorite Iridium plug, their part number 4085.
     
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  16. Carb adjustments

    So is this about the best way to go? Besides also having a reed intake from JNMotors
    You were saying the stock carburetor is suck a pain to adjust is this one the best route?
    I'm sure I can find it on the forum somewhere,but why not be a real nOOb if im going to be one:evilgrin:
     

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    Last edited: Mar 6, 2013
  17. I'm trying to decide myself..
     
  18. jaguar

    jaguar Well-Known Member

    FTR, what carb is pictured there?